1. Field of the Invention
This invention relates to the field of welding sections of pipe together to form a long, continuous pipeline. It relates especially to a system whereby the welding is done with machines.
2. Background of the Invention
One of the major systems for transporting products such as oil, gas, and water, is by the use of pipelines. These pipelines are usually laid underground and literally crisscross the United States and many other countries. A trench is normally dug by ditch diggers along the prescribed route of the pipeline.
Sections of pipe, e.g. 30 to 60 feet or so, are hauled into the area through which the pipeline is being laid. Ends of adjacent joints of pipe are connected by welding. These welds must be very precise. Even little pinholes in the weld cannot be tolerated. The ends of the pipe are normally beveled to improve the welding. These pipes are clamped together to get as good an alignment between the two sections of pipe as possible. On the inside of the pipe at the welding joints the welding material should form a rather smooth surface next to the interior of the pipe. In any event, the weld on the inside of the pipe should have very little protrusion. Excessive protrusion can cause all sorts of problems when one runs apparatuses down inside the pipe, such as apparatus useful to detect any possible flaw which may have developed in the pipeline. Also, introduced in the pipelines are pipeline pigs which separate one product present in a pipeline from a second. It should be understood that sometimes gasoline will be piped through a pipeline. A plug will be put in to separate the two products, and then crude oil will then be pumped through the same pipe. One must maintain a consistent separation of the two materials.
In order to prevent the protrusion of welded molten welding material into the inside of a pipe, the more common practice today is to make the first or root pass of the weld from inside the pipe. Special elaborate, costly machines are commercially available for this purpose. The cost of renting such elaborate, equipment for working on the inside of a three foot (3') diameter pipe may be as much as $1,200.00 per weld, or the rental could be nearly Two Million Dollars per month. This is a very time-consuming and costly welding procedure. It is seen that there is a need for a better, less expensive way of welding pipe sections together.
In modern pipeline welding, welding bugs are sometimes used as semi-automatic welding machines. In conjunction with the welding bug is a track which is secured about the periphery of the pipe at the point it is desired for the welding bug to rotate around the pipe. The bug has a drive motor which with the help of rollers, drives the bug around the track. The rollers hold the welding bug along the track, even when the welding bug is nearly upside down. Special clamping means are provided to secure the bug to the track. Means are also provided to accommodate different size pipe. The welding bug normally has an oscillator to cause the welding tip to oscillate across the welding puddle.
The bug also has a wire feeder which has a motor which drives the wire through the welding head for the actual welding of the two sections of pipe together.
In operation, the drive motor drives the bug around the track at a selected constant rate of speed. However, when the bug is traveling from 12 o'clock, which is the top of the pipe, to about 9 o'clock, which is midway around, the speed is constant. However, for the balance of the down movement of the welding bug to 6 o'clock, the movement must be speeded up because of the gravity pulling the puddle at a faster rate. In order to accommodate this, in current practice, the bug drive motor is stopped. Then the operator will adjust the speed of the drive motor so that it will be speeded up. He then starts the drive motor, and the welding process continues. The movement of the bug is always stopped when making this change in speed.
Stopping the drive motor causes a loss of time in completing the weld. Other associated problems such as maintaining the continuity of the bead must be considered. However, even with these problems, the procedure just discussed is widely used, mainly because it is better than the prior procedures.
It is therefore one object of this invention to provide an apparatus and system whereby the initial or root welding pass can be made from outside the pipe in which there is no internal protrusion of the welding puddle and in which there is an improved welding system.